In the absence of shielding, 'ordinary' nuclear weapons--those containing kilogram quantities of ordinary weapon-grade (6 percent plutonium-240) plutonium or uranium-238--can be detected by neutron or gamma counters at a distance of tens of meters. Objects such as missile canisters can be radiographed with high-energy x-rays to reveal the presence of the dense fissile core of any type of nuclear warhead, or the radiation shielding that might conceal a warhead. If subjected to neutron irradiation, the fissile core of any type of unshielded warhead can also be detected by the emission of prompt--or delayed--fission neutrons at a distance on the order of 10 meters.